The process of emulating the functionality of a first computer platform (the “target system”) on a second computer platform (the “host system”) so that the host system can execute programs designed for the target system is known as “emulation.” Emulation has commonly been achieved by creating software that converts program instructions designed for the target platform (target code instructions) into the native-language of a host platform (host instructions), thus achieving compatibility. More recently, emulation has also been realized through the creation of “virtual machines,” in which the target platform's physical architecture—the design of the hardware itself—is replicated via a virtual model in software.
Two main types of emulation strategies currently are available in the emulation field. The first strategy is known as “interpretation”, in which each target code instruction is decoded in turn as it is addressed, causing a small sequence of host instructions then to be executed that are semantically equivalent to the target code instruction. The main component of such an emulator is typically a software interpreter that converts each instruction of any program in the target machine language into a set of instructions in the host machine language, where the host machine language is the code language of the host computer on which the emulator is being used. In some instances, interpreters have been implemented in computer hardware or firmware, thereby enabling relatively fast execution of the emulated programs.
The other main emulation strategy is known as “translation”, in which the target instructions are analyzed and decoded. This is also referred to as “recompilation” or “cross-compilation”. It is well known that the execution speed of computer programs is often dramatically reduced by interpreters. It is not uncommon for a computer program to run ten to twenty times slower when it is executed via emulation than when the equivalent program is recompiled into target machine code and the target code version is executed. Due to the well known slowness of software emulation by interpretation, a number of products have successfully improved on the speed of executing source applications by translating portions of the target program at run time into host machine code, and then executing the recompiled program portions. While the translation process may take, e.g., 50 to 100 machine or clock cycles per instruction of the target code, the greater speed of the resulting host machine code is, on average, enough to improve the overall speed of execution of most source applications.
Emulation of the target platform by translation relies on blocks of translated instructions. As long as the emulated target platform memory including the original target platform code is unchanged, the target platform emulation can execute the corresponding translated instructions safely. However, certain sections of target code may be modified during normal operation of the target platform. As a result, a corresponding area of the target system memory is changed when the code is modified during operation. To emulate this, the host system may respond to a change in an area of memory by invalidating the corresponding translated target platform instructions. The potentially modified target platform instructions must then be retranslated. However, not all of the code in memory may have been changed and retranslating whole sections of previously translated code when only a few blocks are invalid can take up extra time and processor resources.
Thus, there is a need in the art, for a method and system for translation block invalidation that overcomes the above disadvantage.